Currently, with increasing awareness of health, people are more and more aware of harms caused by cervical vertebra problems. In order to determine health conditions of a cervical vertebra, an accurate measurement needs to be made on the cervical vertebra movements. The cervical vertebra movements are quite complex, including head-up, head-down, head flat turn from left/right to right/left (eyes look straight ahead, head turns, and eyes keep a unchanged vertical distance from the ground), and head rotation from left/right to right/left (eyes look straight ahead, head turns, and the vertical distance between eyes and the ground changes), and so forth. In the prior art, an angular velocity sensor can be used to measure the cervical vertebra movements. Usually, the angular velocity sensor makes measurements within a cycle of the cervical vertebra movements. Specifically, the angular velocity sensor measures a range of the cervical vertebra movements, and then the range is averaged to compute an average angle offset. As the angular velocity sensor measures an average value for the cervical vertebra movements, a real time angle monitoring on the user cannot be achieved. In addition, when an angular velocity sensor is used for measurement, a beginning point and an ending point for the cervical vertebra movements need to be determined. A beginning state where the cervical vertebra of the user is not upright will lead to a measurement error, thus decreasing measurement accuracy.